At present, a UE can access an Evolved Packet System (EPS) via a third generation partnership project (3GPP) access network and also via a non-3GPP access network. Offloading of mobile traffic through a non-3GPP access, such as Wi-Fi access (e.g. via wireless local area network (W-LAN) access points), can be used by network operators to provide a best service to final users, who can use the higher bandwidth Wi-Fi network when the performance or quality that can be offered by, for example, a 3GPP access network is not enough for the services required.
Additionally, some operators are considering Wi-Fi as a coverage extension to their networks, complementing the radio coverage by means of Wi-Fi access points, not only in their home networks but also when roaming. For example, some international roaming programs for mobile subscribers connect automatically to Wi-Fi hotspots via subscriber identity module (SIM) authentication when roaming abroad. Further, specific international Wi-Fi hotspots may be designated and those hotspots may be accessed seamlessly using SIM-based credentials on a smartphone or laptop, obviating the need for a user to launch a client or enter a username and password to gain Wi-Fi hotspot access.
Therefore, there is a trend towards mobile operators leveraging Wi-Fi not just for domestic offloading to ease congestion but in a roaming scenario as well to give better roaming rates to end users and a better user experience.
For access network selection, a new functionality called an Access Network Discovery and Selection Function (ANDSF) has been defined by several 3GPP specifications. In particular, the functionality of the ANDSF is described, for example, in 3GPP specification TS 23.402 v12.2.0, or by the 3GPP specification TS 24.302 v12.2.0. Details of the data that can be managed by the messages exchanged between an ANDSF and a UE are described, for example, in the 3GPP specification 3GPP TS 24.312 v12.2.0.
The ANDSF may be thought of as a control node operable to send to a UE access network discovery and selection policy messages comprising access network policy information, wherein the access network policy information is usable by the UE so as to allow it to, for example, change a data connection from a first radio access network to which the UE is connected (e.g. a data connection established between the UE and a 3GPP or non-3GPP access network) to a second access network. The ANDSF is an example of a control node operable to control access by a UE to access networks.
Typically, an ANDSF contains data management and control functionality necessary to provide network discovery and selection assistance data to the UE over the S14 interface in accordance with operator policy. An ANDSF can access a subscriber profile stored in a User Data Repository (UDR) by means of Ud interface.
Typically, an ANDSF may be aware of the access points available (for example, Wi-Fi and/or 3GPP) in an operator network, and their geographical distribution. For this purpose, a centralised database, such as a geodetic database, stores information about the different location areas and the operator cells and access points within each location area. This information can be accessed by all the ANDSFs deployed in a network to determine the Wi-Fi networks that can be discovered in the vicinity of each cell.
Access network policy information comprising, for example, information on whether 3GPP or non-3GPP access network should be used at a given location, is downloaded to a UE from an ANDSF. The download is dependent on triggers configured in the UE (PULL operation mode) or on triggers configured in the ANDSF (PUSH operation mode).
An ANDSF can provide some triggers for the UE to initiate retrieval of new access network policies by making use of the UpdatePolicy flag as specified in the TS 24.312 v12.2.0. Typically, a trigger provided to the UE may be based on the value of the UpdatePolicy leaf, as defined in 3GPP TS 24.312 v12.2.0, which may be used by the UE to determine whether or not to request update policies when the UE leaves a determined validity area relating to the current access network policy.
Typically, there are three types of information provided by the ANDSF:                Inter-system mobility policy (ISMP)        The ISMP is an access network policy comprising a set of operator-defined rules and preferences that affect the inter-system mobility decisions taken by a UE. The UE uses the inter-system mobility policy when it can route IP traffic only over a single radio access interface at a given time, for example, when it is not Internet Protocol (IP) Flow Mobility (IFOM) capable or its IFOM capability is disabled        Access network discovery information        Upon UE request, the ANDSF may provide a list of access networks available in the vicinity of the UE for all the access technology types requested by the UE, if any are requested        Inter-System Routing Policy (ISRP)        The ISRP is also an access network policy. The ANDSF may provide a list of Inter-System Routing Policies to a UE that are capable of routing IP traffic simultaneously over multiple radio access interfaces. The UE uses the inter-system routing policies when it can route IP traffic simultaneously over multiple radio access interfaces, for example, when it is an IFOM capable UE with the IFOM capability enabled or a Multi-Access Packet Data Network (PDN) Connectivity (MAPCON) capable UE with the MAPCON capability enabled        
An ANDSF may take access selection decisions based on different criteria. Some identified use cases include:                Based on information related to current UE location: a UE that is attached to the 3GPP access network is instructed by the ANDSF via the S14 reference point to select Wi-Fi as the access network when the UE is at the current UE location or when the UE moves out of the current UE location        Based on congestion: selection of Wi-Fi as the access network when the subscriber moves to a congested cell or selection of 3GPP access when Wi-Fi is congested        Based on subscription information        Based on time: the ANDSF selects between 3GPP access and Wi-Fi access depending on time of day—for example, Wi-Fi may be selected only at certain periods of time during the day where it is known that congestion of 3GPP access is foreseen        
Two different procedures are defined, Push and Pull mode, which are described below.
In pull mode operation, UE to ANDSF communication is initiated by the UE:                The UE discovers the ANDSF via Domain Name System (DNS) lookup or Dynamic Host Configuration Protocol (DHCP)        The UE sends a query to the ANDSF to retrieve or update policy data and/or information about available access networks        The UE may provide its location information (for example, cell identities) to the ANDSF        The ANDSF provides the UE with policy data and/or information about available access networks based on the current UE location        The UE performs network detection and selection taking into account the access network specific requirements and the UE's local policy, along with the information provided by the ANDSF        
In push mode operation, the UE to ANDSF communication is initiated by the ANDSF:                The ANDSF sends a Wireless Applications Protocol (WAP) Push message over SMS bearer towards the UE        The UE sends a query to ANDSF to retrieve or update policy data and/or information about available access networks        The UE may provide to the ANDSF the UE's location information (for example, cell identities)        The ANDSF provides the UE with policy data and/or information about available access networks        The UE performs network detection and selection taking into account the access network specific requirements and the UE's local policy, along with the information provided by the ANDSF        
Triggers for push mode operation are implementation dependent in the ANDSF.
The access network policy information transmitted to the UE by the ANDSF over the S14 interface may comprise a validity area (see TS 24.312), which defines the area where a policy rule is valid. This means that the ANDSF downloads to the UE access network selection rules and the area where a rule is applicable. Out of this area the rule shall be discarded. For example, the ANDSF may indicate to the UE that Wi-Fi access has preference over Long Term Evolution (LTE) only in a certain area.
Location granularity can be at different levels and depends on the radio access type. For example, for 3GPP radio access types the following location identifiers apply:                For Global System for Mobile Communications (GSM) Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN): Location Area Code (LAC) and GERAN Cell Identifier (GERAN CI)        For Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN): UTRAN Cell Identifier (UTRAN CI)        For Evolved UTRAN (E-UTRAN): Tracking Area Identifier (TAI) and E-Utran Cell Global Identifier (ECGI)        
As used herein, the term “location area” encompasses a set of base stations that are grouped together to optimise signalling. A location area may be an area in which, after having performed a location update once, MSs may roam without being required to perform subsequent location updates for reasons of location change. A location area may comprise one or more cells. This concept is applicable in 2G and 3G 3GPP access. In 4G access the term “tracking area” may be used instead.
As used herein, the term “tracking area” may define an LTE counterpart of the location area and routing area. A tracking area may be defined as a set of cells.
From the above, it will be understood that the terms location area and tracking area are similar and generally relate to similar features of different network technologies. Therefore, the terms (and any associated terms) are used interchangeably herein.
As used herein, the term “routing area” may be a packet switch domain equivalent of the location area or tracking area. A “routing area” is typically a subdivision of a “location area”.
Typically, the UE is configured to trigger in pull mode the retrieval of policies whenever there is a location change. The ANDSF cannot send to the UE all the policies available in the operator network since this would represent an unmanageable amount of information for the UE. Therefore the ANDSF typically only sends to the UE the policies applicable to the area where the UE is located. Therefore, the UE requests new access network policies from the ANDSF at any location change, even when no policies apply to the new location area. This mechanism is inefficient when the UE moves into areas for which there is no access network policy information in the ANDSF, and results in an unnecessary increment in the signaling between the UE and the ANDSF.